#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
#include<math.h>
int main(void)

{
	float x1, x2, y1, y2;
	float dist;
	scanf("%f%f%f%f", &x1, &x2, &y1, &y2);
	dist = sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
	printf("%.2f\n", dist);
	return 0;
}
